The present invention relates to systems for conditioning, i.e. heating and/or cooling, the air of a selected area, e.g. a room in a house or other building structure, and, more particularly, to such a system that employs separate refrigeration units respectively for heating and cooling.
Prior systems for conditioning the air of a building, such as a house, have included a number of inefficiencies, and with the present effort to conserve energy it is desirable to minimize and/or eliminate such inefficiencies. For example, in connection with combination whole-house heating and air conditioning systems a common blower and air duct system is used to convey heated or cooled air throughout the house. Heat generated by the blower motor, which usually is exposed to the air flow, reduces system efficiency during the cooling operation, and substantial losses usually occur through duct walls before the heated or cooled air even reaches intended discharge vents. Heat also may be lost where ducts pass through slab floors. Moreover, zone control is difficult and inefficient because it is usually obtained by damper adjustment, which unbalances the system and reduces blower optimization.
In view of the depletion and increased cost of energy resources, the recent trend, particularly in home heating and cooling, has been toward the use of electric heat pumps, which typically have a heating seasonal coefficient of performance (C.O.P.) of 1.5 to 1.8 in 6000 to 7000 heating degree day areas. Comparatively electric resistance heating systems have a less efficient C.O.P. of 1. A heat pump for providing adequate heating with the indicated higher C.O.P. efficiency typically includes a refrigerant system with condensation coils, evaporation coils and a reversing valve, which enables reverse system operation to obtain room air heating or cooling, as desired. To achieve the 1.5 to 1.8 C.O.P. the refrigerant system of the heat pump is sized for the cooling load in the house, and such system is reversed for heating so that the evaporator coil becomes the condensor coil thereby giving off heat to the air handler exchange coils. Where the cooling load is substantially less than the heating load, as is the usual case in cool climate areas, the compressor sizing is inadequate to handle the total heat load. To overcome such inadequacy resistance heat is ordinarily added in series with the condenser coil when necessary, which lowers the heating C.O.P. of the system. Moreover, the reversing or switch over valve in the refrigerant system also reduces system efficiency by about 5%. Similarly, in high cooling and low heating climates, conventional heat pumps are not wholly efficient because of the heating and cooling capacity unbalance.